OFFSET
1,2
COMMENTS
Let n be a concatenation of consecutive natural numbers, starting from 1. Is n ever a prime number? [See A007908 for much more about this question. - N. J. A. Sloane, Dec 20 2022]
a(5) has 167 digits. There are no further terms 123...n for n <= 1000 (123...1000 has 2893 digits). - Harvey P. Dale, Dec 20 2022
EXAMPLE
12 is a term since it is the concatenation of 1 and 2, and 12+1 = 13 is prime.
123456 is a concatenation, starting with 1, of consecutive natural numbers and 123456 + 1 = 123457 is prime.
k = 123456789101112131415161718192021222324252627282930 is a term since k+1 = 123456789101112131415161718192021222324252627282931 is prime.
MATHEMATICA
Select[Table[FromDigits[Flatten[IntegerDigits/@Range[n]]], {n, 100}], PrimeQ[#+1]&] (* Harvey P. Dale, Dec 20 2022 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Joseph L. Pe, Apr 03 2002
EXTENSIONS
Corrected by Harvey P. Dale, Dec 20 2022.
Edited by N. J. A. Sloane, Dec 20 2022
STATUS
approved